When he's feeling fatigued on the floor, and there have been a lot of those nights lately, you'll catch Alonzo Mourning glancing down at his wrist like a weary marathoner checking his time. In place of a watch, however, he wears a $1 band of yellow rubber embossed with a message capable of unlocking small miracles: livestrong. "When I'm tired on the court," says Mourning, "I think about what [Lance Armstrong] had to go through, and it's far worse than me getting tired, O.K.? It's far worse than my transplant surgery, and it just casually reminds me, Come on, let's get it done." ¬∂ Since shortly after the 2000 Olympics, when he learned he had focal glomerulosclerosis, a life-threatening disease that scars the kidneys and impairs their ability to filter bodily wastes, Mourning has drawn strength from three books. One is the Bible, and the other two were written by Lance Armstrong. If Armstrong was able to overcome testicular cancer that had spread through his body and win a record seven Tours de France, then Mourning doesn't believe he's asking too much of himself to help drive the Miami Heat to its first championship. As he approached the two-year anniversary of his Dec. 19, 2003, kidney transplant, Mourning was leading the league in both shooting (a career-high 56.7%) and blocked shots (with 3.71 per game). He was also averaging 10.7 points and 7.9 rebounds while keeping the Heat (11-10) atop the admittedly weak Southeast Division during the absence of Shaquille O'Neal, who missed 18 games with a high right ankle sprain before returning Sunday. "He's a warrior, a f------ warrior," Portland coach Nate McMillan said after the Heat beat his Trail Blazers in late November. "He didn't play tonight like a guy who went through [a kidney transplant]."

"If you went on merit right now, I'd have to think he'd be the starting center in the All-Star Game," Stan Van Gundy said last week before he was replaced by Pat Riley as Heat coach on Monday (page 60). "He won't be because he's not on the ballot, but by merit he should be."

Mourning has come up big enough to fill O'Neal's colossal shoes. In a Nov. 26 loss to Orlando, he produced 21 rebounds and 15 points. Two nights later he blocked nine shots in 24 minutes as the Heat wiped out the visiting Knicks. "One of the challenges for Shaq coming back will be to pick up his defense so that [the Heat doesn't] lose a lot of ground there," added Van Gundy. "Zo set the bar very high from a defensive standpoint."

With the return of Shaq, Riley will most likely experiment with a Twin Towers arrangement against big lineups but limit Mourning to about 20 minutes per game. Having watched Mourning play just under 30 minutes per game thus far, Riley worries that his center's increased workload puts him at risk. "We're concerned about him breaking down--and if he reads this quote he might want to grab me by the throat," says the Miami coach. "We can't let his huge heart and stubbornness get the best of him."

USC has won 34 straight, Texas 19 in a row. The two teams have been ranked first and second, respectively, since the first preseason polls came out. When the Trojans and the Longhorns meet in the Rose Bowl on Jan. 4, these seven matchups will go a long way in determining the national champion. Which player will get the upper hand on the opponent lined up across from him?

The return of Mourning's defensive dominance has been accompanied by the familiar scowl that terrorized foes before his kidney disease was diagnosed. So, naturally, he's amused by the sympathy he's receiving from opponents such as the Trail Blazers' 7'1" Joel Przybilla, who recently knocked Zo to the floor, then asked if he was O.K. "That was funny," Mourning says. "Anybody I've knocked to the floor, I've never asked them were they O.K. 'Am I O.K.? I'm fine, Joel.'''

Przybilla, of course, should have known Mourning was fine, having earlier watched him chase spry 20-year-old point guard Sebastian Telfair along the baseline like a grizzly in pursuit of a hummingbird. Telfair shoveled a pass to Przybilla, who took one step and rose for a two-handed dunk--only to have the old man suddenly leap in front of him to slap the ball away. "I never saw him," Przybilla says. "I was amazed he got there."

Mourning has made several sacrifices during his renaissance. Before his illness he was a high-maintenance superstar who demanded 40 touches and produced 20 points a night. These days he focuses on the defensive end, where he is most valuable to the Heat. Which is precisely the example an aging, star-laden roster like Miami's needs. Nobody has been more appreciative of Mourning's transformation than Shaq. "I've always said that when it comes to Zo, I've been the biggest hypocrite," says O'Neal. "Whenever I saw him off the court, it was family--'What up, big Zo!'--but on the court I just hated him.

"But now we've turned out to be really close. He's just a fabulous guy--the hardest working big man I've ever seen, a family-dedicated guy, a community-dedicated guy. When it comes to all the feelings I had about him, I was very wrong."

It is a long way from Dec. 19, 2003, when Mourning received a kidney from his 30-year-old cousin, Jason Cooper, an ex-Marine. Numerous potential donors had stepped forward, including Patrick Ewing, for the life-saving transplant, but Cooper was judged to be the best match. Though his life was about to improve dramatically when he woke up from the three-hour operation, Mourning recalls sobbing uncontrollably. "That was the first time I shed a tear throughout the whole ordeal," he says. "I guess after three years, all the tension, all the [uncertainty] that had built up just came out." As he lay in bed that night in horrible pain, IVs hooked up to both arms, the tentacles of tubes and monitors attached to his body, he prayed for strength. "I said, God, if you ever get me back on my feet to where I'm able to work out, I'll do everything I can to take care of myself."

Despite his weakened condition, Mourning began plotting his return to the NBA the next day. The catalyst for his comeback was a meeting with his surgeon, who told Mourning that he had taken the highly unusual step of not cutting abdominal and hip-flexor muscles on the right side below his rib cage. "He said, 'I felt that you might want to use them later,'" says Mourning.

That same day Mourning was instructed to walk down the hallway to promote blood circulation to his new kidney. As he made his way down the ward, he peered into several rooms. In one he saw an older woman recovering from a lung transplant. Farther down the hall was a 15-year-old boy who was receiving a new kidney after having previously undergone a heart transplant. "I remember thinking, Things could be a whole lot worse for you," he says.

Over the next several months, however, Mourning rarely left his Miami home because he was self-conscious about his frail state. ("My strength is my confidence," he says. "I didn't want to go out anywhere with my family because I didn't feel like I could protect them.") In February 2004, two months after the transplant, he was permitted to walk on a treadmill, and a short time later he began bench-pressing 20-pound dumbbells. "My arms were literally shaking trying to push them up," he says.

Today Mourning takes approximately 20 pills daily, including cholesterol and blood-pressure medications to counteract side effects of his antirejection drugs. During practices and games he wears a small plastic shield with foam padding to protect his kidney. Doctors have told Mourning that if he sticks to his current regimen, he is not jeopardizing his long-term health, but he still faces a 30% chance that the disease will recur in the new kidney.

Mourning says his comeback would be a waste of time if he weren't competing for a championship, which explains his much-criticized decision to demand a trade from New Jersey one year into the four-year, $22 million deal he signed with the Nets in July 2003. New owner Bruce Ratner, Mourning argues, took the Nets out of title contention when, in a cost-cutting move, he didn't re-sign forward Kenyon Martin. In December 2004 Mourning did not accompany the team on a road trip, and a week later the Nets packaged him in a trade with Toronto that landed them Vince Carter. Mourning then agreed to a $9 million buyout on his contract that cleared him to sign with Miami.

His machinations damaged his reputation with fans and team executives around the league, but he says they fail to understand his motives. He believes that his illness has afforded him a chance to become the kind of spokesman for kidney research and organ transplants that Armstrong has become for the fight against cancer. He believes that playing for anything less than a title would diminish his contribution. "That's what I marvel at," says Riley. "Most guys who are getting up in years simply quit on the dream, but Zo sincerely wants to win a championship--otherwise he wouldn't be playing."

Says Mourning, who has raised nearly $10 million more through his foundation (www.amcharities.org), "I'm not back to just play basketball," he says. "I'm back to have a positive influence and do something with this opportunity."

• More on Pat Riley's return to the bench at SI.com/NBA.

SI.COM

Ian Thomsen details the bad blood between Mourning and his ex-team at SI.com/NBA.

"I've been the BIGGEST HYPOCRITE," Shaq says. "When it comes to all the feelings I had about Alonzo, I was very wrong."